Field of the Invention
The present invention relates to a power supply apparatus such as an ACDC converter or a DCDC converter, for example, electronic equipment including the power supply apparatus, and a power supply circuit for the power supply apparatus.
Description of Related Art
A time constant and responsiveness of a passive component included in a typical switching power supply decrease in accordance with a level of a withstand voltage. Accordingly, responsiveness to sharp load transient particularly in a high power application-specific power supply apparatus tends to be lower than that in a small power application-specific power supply apparatus. In addition, a power factor correction circuit is essential for regulating an input harmonic, particularly for high power applications, and power factor correction circuits using various control systems have been developed. It is known that such a power factor correction circuit changes an input current in accordance with a pulsating voltage rectified by a diode bridge, so that pulsation occurs at an output current or an output voltage.
For example, FIG. 6 of Patent Document 1 (Japanese Patent No. JP5110197B) shows such an example that an output including pulsation, which is provided from a power factor correction circuit, is stepped down and is smoothed by a smoothing switching converter. Such a technique shown in FIG. 6 is typically called a two-converter system. While a switching converter is efficient on one hand, there are problems of an increased circuit scale and an increased noise due to a large number of components in a switching circuit. Regarding those problems, according to Patent Document 1, a constant-current feedback control circuit that variably controls impedance is connected in series to a light emitting diode (LED) serving as a load, in an effort to miniaturize a power supply apparatus.
In addition, according to Patent Document 2 (Japanese Patent Laid-open Publication No. JP2013-038882A), when an input voltage including pulsation is higher than a predetermined voltage in a power supply apparatus that adopts a two-converter system, a power factor correction circuit is caused to stop and only a smoothing switching converter is allowed to operate. This allows a reduction in loss of a power factor correction circuit, a reduction in size, and an increase in efficiency.